Many flooring systems in residential and commercial buildings may comprise a floor supported by wood or steel joists. In some flooring systems the floor may comprise a finished floor that is disposed above a subfloor. In single-family and multi-family homes and small commercial buildings, the subfloor may comprise a poured concrete slab or be formed from wooden boards or panels that are laid over the joists. In some apartment buildings, larger commercial buildings and other steel-frame buildings, the subfloor may be a steel deck, precast concrete slabs or panels, or poured concrete.
The finished flooring provides a decorative, aesthetically pleasing floor surface. The finished flooring may be wood, such as wood planks, parquet flooring and wood-block flooring, or a resilient material, such as linoleum, asphalt tile, or vinyl or rubber tile or sheet, or carpeting.
Concrete typically comprises a combination of aggregate and a cement binder having a high water content. After mixing, the cement hydrates and eventually hardens into a hard stone-like material. In many cases, the concrete retains a high moisture content that may slowly dissipate from within the concrete over a period of time. In some cases, concrete may also wick moisture from the surrounding environment, such as the ground, into the concrete. Moisture from within the concrete may dissipate upwardly through the concrete and come into contact with the floor.
Hardwood flooring and wood in general are hygroscopic materials. Liquid water and water vapor can enter wood which may cause it to swell and change its shape and size, potentially causing bubbling. If and when the water leaves the wood, the wood can shrink which may result in warp, the development of small cracks in the surface of the wood, twists, bows, or even develop cups or dips within each piece of wood flooring. In some cases, cracks in between pieces of wood may open up as the wood dries.
To help prevent moisture from contacting the finished flooring, it may be desirable to place a moisture barrier between the flooring and the subfloor. The moisture barrier may comprise a thin layer of film adhered to the surface of the concrete. In some applications an underlayment layer comprising a layer of film and a layer of foam, or a polyethylene film/foam laminate, is provided as an underlayment between the concrete subfloor and finish flooring formed of wood. The underlayment levels small irregularities in the top surface of the concrete, provides a small degree of resiliency to the floor system, and provides a vapor barrier to prevent moisture emanating from the concrete subfloor from attacking and deteriorating the finish flooring.
Despite the advantages provided by barrier films and floor underlayments, many barrier films may permit some transmission of water vapor. In some cases, water vapor may be trapped between the flooring and underlayment. This may result in the development of mold, fungus and other growths, leading to odors and other health concerns. In addition, because of the tendency of these underlayments to trap moisture, they may not be usable with wood subfloors which would deteriorate on prolonged exposure to moisture.
In some flooring systems, a temperature gradient may exist between the subfloor and the finished floor. In some cases, this temperature gradient may result in temperature variations within the underlayment. Temperature variations within the underlayment may adversely affect the underlayment. For example, a temperature gradient may cause one or more portions of the underlayment material to prematurely fail, such as the formations of cracks and/or deterioration or delamination of the foam and film layers.
Thus, there exists a need for an improved floor underlayment which provides the cushioning, and floor leveling functions of the prior floor underlayments, but which also permits the controlled escape of moisture from the subfloor so as to avoid the disadvantages associated therewith.